This invention relates to a method for manufacturing a furnace component such as a process tube for a semi-conductor diffusion furnace.
U.S. Pat. No. 3,951,587 discloses semi-conductor diffusion furnace components such as a process tube, paddle and boat consisting essentially of a sintered silicon carbide matrix resulting from the sintering of silicon carbide powder which is made up of approximately 50% by weight of fine silicon carbide having an average particle size of 0.1-8 microns and 50% by weight of coarse silicon carbide having an average particle size of 30-170 microns.
In such semi-conductor diffusion furnace components, since the fine silicon carbide powder has an average particle size of from 0.1-8 microns, the surface areas of the powders is large enough so that impurities can be easily caught thereby.
Also, density and chemical purity of a formed body are important factors for semi-conductor diffusion furnace components.
In general, silicon carbide powder is milled by a vibration type mill or the like and then sieved to thereby yield a starting material having desired particle sizes. During the milling process, however, many impurities are caught to such a degree that silicon carbide powder so produced cannot be suitably used for the purpose of manufacturing high quality semi-conductor diffusion furnace components. Thus, purification treatment such as acid treatment is applied to the silicon carbide. Even with this treatment, however finer powder remains relatively contaminated and cannot be easily purified. For such a reason, it is preferable to use coarse silicon carbide powder from to achieve high quality components. However, if only coarser silicon carbide powder is used, sufficient density and strength for a process tube cannot be obtained.